The principal component in first generation thick film resistor systems was palladium oxide powder. Second generation thick film resistor systems used ruthenium oxide powder. Noble metal resistor paints require noble metal conductors for making microcircuits. The recent increase in the cost of precious metals has made their use prohibitive for many applications. Tin oxide compounds have been used as a major conductive material in resistors for many years. Tin oxide films may be processed by spraying and heating a tin chloride solution; by evaporation or sputtering technology; by chemical vapor deposition; or by thick film technology.
Thick film technology has been used in the electronics industry for more than 25 years. Thick film technology includes printing and firing a resistive paint in a desired pattern upon a suitable substrate. Resistive paints used in thick film technology typically include a conductive or resistive material, a glass frit, and a screening agent. A base metal resistive paint is a resistive paint that has no noble metals included in its composition.
Various materials have been admixed with tin oxide powder to obtain a wide range of resistivity.
Metallo-organics are homogenous solutions in which a metal is linked to an oxygen, a sulfur or a nitrogen atom, which in turn is attached to one or more carbon atoms.
Examples are: ##STR1## where "R" represents an aromatic or aliphatic group. A metallo-organic compound may be called a metal resinate, where the organic portion is derived from resins or other natural compounds. Firing a metal resinate at high temperature will burn out the organic portion to form a metal or metal oxide having atomic or molecular form. A precious metal resinate will yield a metal when fitted in air. A base metal resinate will yield a metal only when fired in an inert or reducing atmosphere. Metallo-organic conductors and resistors have been used for many years, but their use was previously limited to use with precious metals.
Current thick film technology should meet stringent test requirements; exhibit several decades of sheet resistivity; control TCR to within .+-.200 ppm/.degree.C.; and be capable of being fired at a uniform temperature to be commercially acceptable. The higher the firing temperature, the more energy and expense is expended to make the resistor. Therefore, it is advantageous to disclose a resistive paint capable of firing at less than 1,000.degree. C. The resistive paint of the current invention is preferably fired at 900.degree. C..+-.20.degree. C.